Chapter 20, Problem 9A

Interpretation Introduction

Interpretation: The term isomer needs to be explained and the smallest alkane that has a structural isomer needs to be determined.

Concept introduction:Structural isomerism: Describes what occurswhen two moleculeshave the same atomsbut different bonds.

Answer to Problem 9A

Structural Isomers are the compounds having same molecular formula but different atomic arrangements and the smallest isomer is butane.

Explanation of Solution

Structural isomers are the molecules having same formula but different arrangements of atoms.

The smallest isomer is butane.

		Lewis structure	Comment
1.	n-butane	$\begin{array}{l}\text{H}\text{H}\text{H}\text{H}\\ \left|\right|\left|\right|\\ \text{H}-\text{C}—\text{C}—\text{C}—\text{C}-\text{H}\\ \left|\right|\left|\right|\\ \text{H}\text{H}\text{H}\text{H}\end{array}$	The straight chain has 4 carbons atoms and is called n-butane.
2.	isobutane	$\begin{array}{l}\text{H}\\ |\\ \text{H}\text{H}-\text{C}-\text{H}\text{H}\\ \left|\right||\\ \text{H}-\text{C}—\text{C}—\text{C}-\text{H}\\ \left|\right||\\ \text{H}\text{H}\text{H}\end{array}$	If we remove one carbon atom from the parent chain and place it to the second carbon. It has 4 carbon atoms bonded with hydrogen atoms and is called isobutene.

Conclusion

Butane can exist as a straight-chain molecule (normalbutane, or n-butane) or with a branched-chain structure (called isobutane). Because of their different structures, these structural isomers have different properties.